1. Field of the Invention
The present invention relates to a planar stitched write head having a write coil that is insulated by inorganic insulation and, more particularly, to a write head having a second pole tip and coil layer that are planarized with silicon dioxide located between the turns of the coil layer and between the coil layer and the second pole tip.
2. Description of the Related Art
The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm above the rotating disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly mounted on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent the ABS to cause the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head and the pole piece layers are connected at a back gap which is recessed from the ABS. Current conducted to the coil layer induces a magnetic field across the gap between the pole pieces. This field fringes across the gap at the ABS for the purpose of writing information in tracks on moving media, such as a tape in a tape drive or in circular tracks on the aforementioned rotating disk.
Since the second pole tip is generally the last pole tip to pass locations on the circular track of a rotating disk, it is important that the width of the second pole tip be as narrow as possible for increasing the track width density of the write head. The track width density is expressed in the art as tracks per inch (TPI). Research efforts have narrowed this track width thereby increasing magnetic disk drive capabilities from kilobytes to megabytes to gigabytes. An ongoing problem in the art, however, is producing a narrow second pole tip with good side wall definition. The second pole tip is typically made by patterning photoresist that has an opening where the second pole tip is to be plated. Unfortunately, the high topography behind the second pole tip in typical write heads causes light to be reflected toward the ABS during a light exposure step of the photoresist adjacent the desired side walls of the second pole tip. This light exposes photoresist adjacent to the intended side walls which, upon developing, is removed and causes an irregularity when the second pole tip is plated. A main contributor to this high topography is the insulation stack where the coil layer is embedded and a seed layer covering the insulation stack that is highly reflective. A reduction in this topography decreases what is known in the art as "reflective notching" so as to produce a more highly defined second pole tip.
The aforementioned high topography behind the second pole tip also degrades the performance of the yoke portion of the second pole piece which extends from the second pole tip to the back gap if the yoke is deposited by sputtering techniques. When the yoke portion of the second pole piece slopes down from the high topography to the second pole tip, it makes a curve which changes its magnetic properties. Some of these properties are uniaxial anisotropy field (H.sub.K) and coercivity (H.sub.c). Accordingly, it would be desirable to construct a planar second pole piece so that its magnetic properties would not be altered. Still a further problem of the high topography is that after completion of the head a thick overcoat layer is required in order to protect the yoke and pole tip portions of the head.
The aforementioned insulation stack is typically made from various layers of hard baked photoresist. In the construction sequence a layer of photoresist is spun on a wafer which is substantially planarized thereacross. The photoresist layer is then photopatterned with light exposing areas that are to be removed. The photoresist layer is then developed with a developer which causes the exposed areas to dissolve so they can be removed. The layer is then soft baked at a temperature of 90.degree.-120.degree. C. which causes the layer to solidify with rounded edges. After constructing a coil layer on a soft baked photoresist layer one or more additional photoresist layers may be constructed and soft baked in the same manner. Thereafter, the photoresist layers are hard baked at a temperature of 230.degree. C. which hardens the photoresist layers. Photoresist is an organic material that has a different coefficient of expansion than other materials in the head, such as aluminum oxide (Al.sub.2 O.sub.3) employed for the overcoat layer. When the magnetic head is operating within a disk drive its operating temperature is at least above 100.degree. C. This causes the hard baked photoresist insulation stack to expand more than the overcoat layer which causes the overcoat layer to protrude beyond the pole tips at the ABS. This protrusion can ruin the head or severely degrade its performance. Further, the hard baking of the photoresist layers can result in loss of signal amplitude for some read sensors, such as spin valve sensors, in an adjoining read head. The hard baked temperatures cause some intermixing of the materials of the layers which can significantly degrade their performance. Still further, the hard baked photoresist insulation stack has poor heat dissipation which aggravates all of the aforementioned problems.
A recap of the aforementioned problems is as follows:
(1) Difficulty of second pole tip track width definition because of severe topography;
(2) Magnetic property change of a sputtered yoke portion of the second pole piece as it curves over severe topography;
(3) Requirement for thick overcoat deposition;
(4) Protrusion of the overcoat layer at the ABS due to thermal expansion of a hard baked photoresist insulation stack;
(5) Signal amplitude loss of some spin valve sensors due to hard baking of the photoresist layers; and
(6) Inadequate heat dissipation of the hard baked photoresist insulation stack.